1. Field of Invention
This invention relates to the field of river floods control and management, more specifically, it is a method of controlling river flood by means of astronomical tidal current at the estuary (a river mouth open to the sea) to control and discharge floods in upper stream.
2. Description of Related Arts
Floods disaster has been very serious in China. According to the imperfect statistics, there were 1092 major floods during the 2,155 years between 206 B.C and 1949 A.D. i.e. once every two years in average. Countless lives and properties were lost. There is an old saying about the Yellow River “bursts twice every three years, changes of its course once every hundred years”.
From the olden days, Chinese people combat hard with the serious floods, specially, from the foundation of the People's Republic of China. The Chinese government constructed many river conservancy projects. The new measures include both engineering and non-engineering approach. Gradually, a more comprehensive floods control system was founded. As a result, the Yellow River did not have great floods for the past 50 years and the Chinese people were proud of having no major flood problem for 50 years in the yellow river. This is indeed a great achievement in Chinese history. However, we should notice that China had still great difficulties in river flood control. The flood control standard is still not high enough. Whenever there is abnormal heavy rainfall, China is still facing dangerous situations, directly endangering embankments, reservoirs and other hydraulic projects etc. and will still cause catastrophe.
Rich experiences were gained during the long term floods fighting history in China, although nowadays new technology and new materials, enriches and improves the methods of dealing with floods. However, during the great floods at Yangtze River in the year of 1998, there are still more than 9,000 dangerous locations and incidents found on the river banks along the Yangtze River.
For case study, in the year 1999, heavy rainstorm occurred in the tributaries of the Yangtze River upper stream, such as Min River, Tuo River, Jiangling River, Wu River, and also occurred in the Yangtze River middle & lower stream, such as Dongting Lake and Boyang Lake.
As a result, serious floods happened in all sections of the Yangtze River, such as Xiang, Zi, Ruan, and Li in the Dongting Lake area and the Chang River, and Lean River in the Boyang Lake area and so on. Four crests developed at trunk stream of the Yangtze River upper stream consecutively.
The water level of most of the main hydrology station from Yichang to Nanjing along the trunk stream had risen beyond the caution level, among these figures, such as that recorded at the hydrology stations of Shashi, Shishou, Jianli, Lianhuatang, Luoshan, Wuxue, Jiujiang and ChengLingji of Dongting Lake and Hukou of Boyang Lake were approaching the highest historical record. The third highest water level happened at the hydrology stations of Hankou and Datong City. The fact that the flood level reached the record high in most segments of the Yangtze River reviews the fact that the flood conditions is deteriorating continually.
There were local rainstorms at the Yangtze River upper stream in the year of 1999, and floods water levels were reported to have been well above the caution level at Wu River and Min River. The floods at Wu River were very serious. The highest floods level 204.63 m which was 12.63 m higher than the safety pledged level (192.00 m), and 0.12 m higher than the historical highest level (204.51 m in 1955) which happened in June at Wulong (of Chongqing City). The corresponding flow rate recorded was 22,500 m3/s, which was the largest flow rate ever recorded (the old historical largest flow rate was 21,000 m3/s in the year 1964).
Being affected by the tremendous amount of rainfall from Yangtze River upper stream, it was found that a historical biggest floods happened in July 1999 at the Cun Tan (near Chongqing) hydrology station at the trunk stream of Yangtze River upper stream with the floods peak of 180.02 m, which was 0.02 m higher than the caution level (180.00 m), and the corresponding water flow rate was 48,700 m3/s.
Four floods crest were recorded at the hydrology station of Yichang, with the flood peak levels reaching 51.38 m, 52.20 m, 53.68 m, and 51.73 m, and the corresponding flow rate were 46,800, 51,800, 57,200 and 44,200 m3/s respectively. All of these crests were still considered to be ordinary flooding in Yangtze.
Having been affected by the great amount of water from the Yangtze River upper stream and the two major lakes and other branches, the trunk stream water level of Yangtze River middle and lower stream began to rise after mid-June. The water level at the hydrology stations at Shishou and Wuhu was the first to rise beyond the caution level.
The water levels of different river segments from Jianli to Liauhuatang and from Jiujiang to Datong have also risen beyond the caution levels gradually in different stages afterwards, and the important segments from Lianhuatang to Hankou had also reached the caution level.
The highest water level occurred at most of the main hydrology stations along the Yangtze River after mid-July, 1999. The peak water level of 44.74 m at the hydrology station of Shashi in July was the second highest record ever, which was 1.74 m higher than the caution water level (43.00 m), although lower than the historic record of the year of 1998 (45.22 m). The highest water level in July at the Jianli hydrology station was 38.30 m, which was 1.02 m higher than the pledged water level (37.28 m), and was only 0.01 m lower than the historical highest water level (38.31 m in 1998).
The highest water level in July at the Lianhuatang hydrology station was 35.54 m, which was 1.14 m higher than the pledged water level (34.40 m), and was the second highest water level, of actual record in 1998 (35.8 m) . The highest water level in July at Luoshuan hydrology station was 34.60 m, which was 0.59 m higher than the pledged water level (34.01 m), and it was the second highest water level of actual surveying record in 1998 (34.95 m).
The highest water level in July at the Hankou hydrology station was 28.89 m, which was 1.59 m higher than the caution water level and it was the third highest water level (29.73 m in 1954, and 29.43 m in 1998). The highest water level in July at the Jiujiang hydrology station was 22.43 m, which was 2.93 m higher than the caution water level (19.50 m) and it was the second highest water level recorded in 1998 (23.03 m). The highest water level in July at Datong hydrology station was 15.87 m, which was 1.37 m higher than the caution water level (14.50 m).
At present, the overall standard for preventing floods is still not very high. If there are some floods which are concentrated and are developed within a very short period, dangerous flood situations and disasters will be formed. These will bring great lost to the country and the people. If there is a comparatively simple and efficient method to discharge the floods, it will be beneficial to the country and the people and the people in the future generations inside.